<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <canvas id="canvas" style="border: 1px solid #aaa; display: block; margin: 50px auto;">
        当前浏览器不支持Canvas，请更换浏览器
    </canvas>
    <script>
        window.onload = function () {
            var canvas = document.getElementById("canvas");

            canvas.width = 800;
            canvas.height = 800;

            var context = canvas.getContext("2d");

            context.fillStyle = 'black';
            context.fillRect(0, 0, canvas.width, canvas.height);
            for(var i = 0; i < 200; i++) {
                var r = Math.random() * 10 +10;
                var x = Math.random() * canvas.width;
                var y = Math.random() * canvas.height;
                var a = Math.random() * 360;
                drawStar(context, r/2.0, r, x, y, a);
            }
        }

        function drawStar(cxt, r, R, x, y, rot) {
            cxt.beginPath();
            for (var i = 0; i < 5; i++){
                cxt.lineTo(Math.cos((18 + i*72 - rot)/180*Math.PI)*R + x, -Math.sin((18 + i*72 - rot)/180*Math.PI)*R + y);
                cxt.lineTo(Math.cos((54 + i*72 - rot)/180*Math.PI)*r + x, -Math.sin((54 + i*72 - rot)/180*Math.PI)*r + y);
            }
            cxt.closePath();

            cxt.fillStyle = '#fb3';
            cxt.strokeStyle = '#fd5';
            cxt.lineWidth = 3;
            cxt.lineJoin = 'round';

            cxt.fill();
            cxt.stroke();
        }
    </script>
</body>
</html>